The present invention relates to an image pickup apparatus applied to a videotape recorder which is equipped with a camera having a digital zoom function and an electronic still camera having a frame electronic shutter function, etc., and the apparatus is equipped with a charge coupled device (CCD) having a complementary color checkered filter.
As for the CCD used in the above image pickup apparatus, a CCD as shown in the technical report of the Television Institute (Page 79-84 of Feb. 28, 1989 issue) is capable of full line reading by increase of the vertical transfer gates from 2 to 3 for one picture element.
And as for the complementary color checkered filter with which the CCD is equipped, there is a color filter arrangement type as shown in FIG. 4 and field reading is carried out as shown in the drawing. In field A, electric charges are mixed in a pair of A1 line or A2 line (In field B, in a pair of B line). Therefore, an order of electric charge coming out of a horizontal shift register (Hreg) as signal in A1 line is EQU {(G+Cy), (Mg+Ye), (G+Cy), (Mg+Ye)}.
A luminance signal (Y signal) and a color difference signal are constructed by treating the above signals. The Y signal is obtained by adding a field pair in the line to a neighboring field pair, and the color difference signal is obtained by taking a field pair in the line from a neighboring field pair. That is, the Y signal is obtained based on the approximate signal shown in the following equation; ##EQU1## The color difference signal is obtained based on the approximate signal shown in the following equation; ##EQU2## And in A2 line, an order of a signal coming out of a Hreg is {(Mg+Cy), (G+Ye), (Mg+Cy), (G+Ye)}. The Y signal constructed with these signals is shown in the following equation; ##EQU3## Thus, the Y signal of A1 line and of A2 line are balanced because of the same construction.
Similarly, the color difference signal is approximated by the following equation; ##EQU4## After all, R-Y and -(B-Y) are obtained as the color difference signal alternately in linear order. Field B is treated in the same manner.
In the above mentioned prior art, when full line reading of CCD, to which color coding is applied by a complementary color checkered filter, is made, color can be demodulated by means of the same color demodulation process as a case of field reading effected by mixing two lines by delaying one horizontal line. However this is the color difference line-sequential system, if line numbers are (n).about.(n-5), the color difference signal is shown as follows; ##STR1## Two kinds of the color difference signals appear in two successive lines alternately like EQU [R-Y], [R-Y], [B-Y], [B-Y], [R-Y], [R-Y]
Further delay circuitry corresponding to two lines is necessary for synchronization as shown in the above right hand. (The color difference signal in the number n line is composed of [R-Y] obtained from (n) and (n-1) and [B-Y] obtained from (n-2) and (n-3). One line color signal contains four lines of CCD output signals, so there is a problem to cause the deterioration of vertical resolution of the color signal.